Differential summing mechanisms, or mechanical integrators, are commonly used to combine two or more rotary input signals, to generate a proportionate cumulative output signal. A particularly important application for such devices is in the variator section of the mechanical computers that are used for fuel pumps, by which the unit volume price of the fuel product can be selectively set. Signals proportionate to the digits or places of the price are generated, normally through the use of separate range arm assemblies that are selectively positionable in engagement with one of the elements of a gear stack or cone gear, which signals are combined in the summing mechanism to generate a signal that is representative of the total unit price.
Typically, such mechanical integrators consist of at least two gear plates coaxially mounted upon a shaft, one of which plates has an external circumferential tooth formation and rotatably mounts, in diametrical positions, a pair of compound planetary gears; the other gear plate will have both external and internal circumferential tooth formations. Rotary motion of the first gear plate is transmitted directly to the mounted planetary gears, and rotary motion of the other plate is transmitted to the same gears through the internal tooth formation. Consequently, the output from the planetary gears (which can be taken from a single pinion driven by them), will be proportionate to the sum of the inputs applied to the two gear plates. Such summing mechanisms may be of multiple effect, and may include stacked planetary gear sets and associated gear plates, such as to provide a cumulative output proportionate to the multiple digits of a posted unit volume fuel price.
For some applications, summing differential mechanisms of the type described have been found to be excessively large, in terms of diameter as well as face-to-face thickness. While it is conceivable that the dimensions of the unit could be reduced simply by using thinner and smaller parts, the torque loadings to which such devices are subjected in operation will make such an approach impractical in many instances. Thinning the parts will obviously weaken them. Reducing the number of teeth on the planetary gears, so as to permit size reduction, will have the same effect, due to the undercutting at the base of each tooth which tends to result from the provision of the required clearance for mating teeth. Such a loss of strength is particularly undesirable in view of the fact that each tooth will be required to carry a greater proportion of the torque load. Furthermore, since the planetary gears utilized in such an integrator normally have even numbers of teeth, the elimination of one tooth will obviously produce an odd number; this will introduce even further difficulties into the design of the unit.
In addition, there are instances in which it is desired to utilize, as the source for one of the input signals, the shaft upon which the integrator is mounted. It is not believed that prior summing mechanisms have adequately accommodated this desire.
Accordingly, it is a primary object of the present invention to provide a novel differential summing mechanism which is capable of being fabricated in relatively small sizes, without reduction in the capability of the unit to withstand normal torque loadings.
It is a more specific object of the invention to provide such an integrator in which the number of planetary gears is increased to three.
Another object of the invention is to provide an integrator having the foregoing features and advantages, in which each of the planetary gears has an odd number of teeth in its circumferential tooth formations.
Yet another object of the invention is to provide such an integrator to which one of the input signals can be taken from the shaft on which the mechanism is mounted.